Victoria in September 2008 An unusually dry September

September rainfall was well below the long-term (all years
of record) normal in all Districts, largely on account of the persistence of
high pressure systems over southeastern Australia, and the relatively few
periods of frontal or cyclonic activity and also the fact that there has been little moisture associated with those fronts that did affect us.

Daytime temperatures have averaged above the long-term normal in most
Districts, whilst overnight temperatures have been mostly below normal in the
north, and near normal in the south. The relatively cold nights over inland
Victoria have been a consequence of the mostly clear skies, allowing maximum
radiational cooling.

In the Melbourne CBD, the average minimum temperature has been 9.7 deg C (1.8
deg C above the long-term average over all years of record), whilst the average
maximum temperature has been 19.4 deg C (2.2 deg C above the long-term average).
Total September rainfall was 12 mm, well below the long-term average of 57.9 mm. The 12 mm reading represents the lowest September
total on record - previous record 13.4 mm in September 1907.

The Melbourne CBD is usually warmer than the suburbs on account of what is
known as the "heat island
effect", a feature of the inner areas of most major cities. This effect occurs
on account of the ability of the buildings and roads to absorb heat (and then to
re-radiate it back into the atmosphere) more effectively than grassland and
forest.

This point is effectively illustrated by the fact that, away from the city
centre at Melbourne Airport, average temperatures were not as high. The average September 2008 minimum temperature at the Airport was 7.0 deg
C (the same as the long-term average), whilst the average September 2008
maximum temperature was 18.4 deg C (1.9 deg C above the long-term
average).

Notes

This statement has been prepared based on information available at
9 am on Thursday 2 October 2008.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Normals are long-term means based on observations from
all available years of record, which vary widely from site to site.
They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median
is sometimes more representative than the
mean
of long-term average ("normal") rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
normal in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of normal shows how much rain has fallen this time as a
percentage of the long-term mean.